Nox sensor with improved selectivity and sensitivity

Abstract

A NO x sensor and a method of manufacturing a NO x sensor array. The NO x sensor includes a base substrate, a plurality of potentiometric sensors, and a plurality of connectors. The plurality of potentiometric sensors are coupled to the base substrate. Each potentiometric sensor generates a potential difference in response to the presence of NO X in a gas specimen. The plurality of connectors are coupled to the plurality of potentiometric sensors. The plurality of connectors connect the plurality of potentiometric sensors to combine the potential differences of the plurality of potentiometric sensors to produce a combined potential difference indicative of a level of NO x within an ambient gas specimen. Use of a filter and appropriate temperature control of filter and sensor minimizes interference from contaminants.

1 . A NO x  sensor comprising:
 a base substrate;   a plurality of sensors coupled to the base substrate, each sensor to generate a potential difference in response to the presence of NO x  in a gas specimen; and   a plurality of connectors coupled to the plurality of sensors, the plurality of connectors to connect the plurality of sensors to combine the potential differences of the plurality of sensors to produce a combined potential difference indicative of a level of NO x  within an ambient gas specimen.   
     
     
         2 . The NO x  sensor of  claim 1 , wherein the plurality of sensors comprises a plurality of potentiometric sensors. 
     
     
         3 . The NO x  sensor of  claim 2 , wherein the plurality of connectors are connected to the plurality of potentiometric sensors to connect the plurality of potentiometric sensors in series, wherein the combined potential difference comprises a sum of the potential differences of each of the potentiometric sensors. 
     
     
         4 . The NO x  sensor of  claim 3 , wherein each of the potentiometric sensors comprises a sensing electrode and a reference electrode. 
     
     
         5 . The NO x  sensor of  claim 4 , further comprising:
 a first electrical lead coupled to the sensing electrode of a first potentiometric sensor within the series of potentiometric sensors; and   a second electrical lead coupled to the reference electrode of a last potentiometric sensor within the series of potentiometric sensors;   wherein the combined potential difference is measurable at the first and second electrical leads.   
     
     
         6 . The NO x  sensor of  claim 5 , further comprising a third potentiometric sensor coupled between the first and last potentiometric sensors within the series of potentiometric sensors, wherein the sensing electrode of the first potentiometric sensor is connected to the reference electrode of the third potentiometric sensor, and the sensing electrode at the third potentiometric sensor is connected to the reference electrode of the last potentiometric sensor. 
     
     
         7 . The NO x  sensor of  claim 6 , wherein the sensing electrode comprises tungsten oxide (WO 3 ). 
     
     
         8 . The NO x  sensor of  claim 4 , wherein the reference electrode comprises platinum (Pt). 
     
     
         9 . The NO x  sensor of  claim 8 , wherein the reference electrode comprises platinum (Pt) coated with platinum zeolite (PtY). 
     
     
         10 . The NO x  sensor of  claim 2 , wherein each of the potentiometric sensors comprises an electrolyte substrate, wherein the electrolyte substrate comprises an oxygen-ion conducting ceramic. 
     
     
         11 . The NO x  sensor of  claim 10 , wherein the electrolyte substrate comprises yttria-stabilized zirconia (YSZ). 
     
     
         12 . The NO x  sensor of  claim 2 , wherein the plurality of potentiometric sensors comprises at least three potentiometric sensors. 
     
     
         13 . The NO x  sensor of  claim 2 , wherein each of the connectors of the plurality of connectors comprises platinum (Pt). 
     
     
         14 . A method for manufacturing a NO x  sensor array, the method comprising:
 disposing a plurality of electrolyte substrates on a base substrate;   disposing a sensing electrode on each electrolyte substrate;   disposing a reference electrode on each electrolyte substrate; and   connecting, in a series configuration, each of the sensing electrodes, other than a first sensing electrode, to corresponding reference electrodes, other than a last reference electrode, on adjacent electrolyte substrates.   
     
     
         15 . The method of  claim 14 , further comprising using a metallic paste to dispose the electrolyte substrates on the base substrate. 
     
     
         16 . The method of  claim 14 , connecting the electrolyte substrates in series with a plurality of platinum (Pt) wires. 
     
     
         17 . The method of  claim 14 , painting the sensing electrode onto the electrolyte substrate, wherein the sensing electrode comprises platinum (Pt). 
     
     
         18 . The method of  claim 14 , painting the reference electrode onto the electrolyte substrate, wherein the reference electrode comprises tungsten oxide (WO 3 ). 
     
     
         19 . A sensing system to measure NO x  in a gas specimen, the sensing system comprising:
 a sensor array comprising a plurality of NO x  sensors coupled in series, the sensor array to detect a nitrogen oxide compound in a gas specimen;   a filter to remove a contaminant compound from the gas specimen; and   a plurality of temperature-control devices to maintain the gas specimen at a substantially consistent temperature at the sensor array.   
     
     
         20 . The sensing system of  claim 19 , wherein the plurality of NO x  sensors comprise substantially similar materials and structures. 
     
     
         21 . The sensing system of  claim 20 , wherein each of the NO x  sensors comprises a sensing electrode and a reference electrode, and wherein the sensing electrodes and the reference electrodes of the adjacent NO x  sensors, respectively, are coupled together to produce a combined potential difference indicative of a sum of potential differences of the plurality of NO x  sensors. 
     
     
         22 . The sensing system of  claim 21 , wherein the sensor array further comprises a plurality of connectors coupled to the plurality of NO x  sensors, the plurality of connectors to connect the plurality of NO x  sensors in series. 
     
     
         23 . The sensing system of  claim 19 , wherein the filter is further configured to remove the contaminant compound from the gas specimen prior to introduction of the gas specimen at the sensor array. 
     
     
         24 . The sensing system of  claim 19 , wherein the sensor array is calibrated to detect parts per million (ppm) and sub-ppm quantities in the gas specimen. 
     
     
         25 . The sensing system of  claim 19 , wherein the sensor array is further configured generate an electrical potential difference in response to detection of the nitrogen oxide compound. 
     
     
         26 . The sensing system of  claim 19 , wherein the plurality of temperature-control devices are further configured to maintain a temperature difference between the sensor array and the filter.